Ukip is facing new turmoil after former MP Mark Reckless said he was quitting the party to join the Conservative group in the Welsh Assembly.

Announcing the move, Mr Reckless, who originally defected to Ukip from the Tories in 2014, said he was delighted to have made the Tories the official opposition in Wales but faced criticism from Ukip, who described the move as "disappointing".

In response to claims he should stand down because he was elected through the party list system, which meant voters were voting for the party rather than individual candidates, Mr Reckless told the Press Association he would "love to hold a by-election as I did previously so that I can test my decision and get the voters' support for what I am doing".

He said: "Unfortunately, the proportional representation system we have in Wales doesn't allow that."

Ukip party chairman Paul Oakden said Mr Reckless should give up his seat for a Ukip candidate.

"Having been elected as a Conservative in Rochester and Strood, Mark didn't think it right to sit as an MP for another party without asking the electorate for their endorsement in a by-election.

"A position that was as right as it was honourable," he said.

"It is now incumbent on Mark Reckless to relinquish a position he has only by virtue of a Ukip mandate. The position should go to the next Ukip candidate on the regional list."

Mr Reckless: "I would say many of the people who voted Ukip in South East Wales last year, now the Conservatives are delivering Brexit and we are the main opposition in the Assembly, I think are, like me, leaving Ukip and coming over to the Conservatives now we have achieved what we wanted in Ukip, which was a successful referendum to leave the EU."

Mr Reckless said he had been "thoroughly impressed by the performance and discipline of Andrew RT Davies and the Welsh Conservative group" since joining the Assembly last May.

He added: "The Prime Minister's leadership since taking office has also been exemplary and she has been steadfast in her position to deliver on the wishes of the people of Wales and the United Kingdom, building a united country that works for everyone and not just the privileged few."

His defection is a further blow for Ukip after its only MP Douglas Carswell, another defector from the Tories, announced he was leaving to sit as an independent.

Mr Reckless, who said he was friends with Mr Carswell, denied he had faced any pressure from him to leave Ukip.

Mr Reckless originally joined Ukip in 2014, but after winning a by-election in his Rochester and Strood seat, he was voted out of the Commons in the 2015 general election.

He was subsequently elected to the Welsh Assembly on a Ukip ticket in May 2016.

The Conservatives confirmed that while Mr Reckless had joined the party's group in the assembly, making them the second largest party after Labour, he had not actually rejoined the party.

Mr Reckless said he had not applied to rejoin, nor had he " asked for anything at the UK level at all".

He said: "I think there are still some sore wounds and people who feel that I've stood against the party in previous times and it's not for me to waltz back into the party with any sense of entitlement.

"I need to knuckle down and support Andrew RT Davies.

"I'm delighted I've made the Conservatives the official opposition in Wales and we want to support Theresa May and the UK Government with what they're doing.

"I think the Conservatives will be in a much stronger position now in Wales to work with Theresa May and get the best deal for Wales."

Mr Reckless added his new colleagues in the Tory group had reacted positively to his decision and said he would be "delighted to pitch in any way I can" in order to help the party do well in next month's local elections in Wales.

In a letter to Mr Davies, the assembly presiding officer Elin Jones said, as Mr Reckless was no longer a member of Ukip, that he "can be treated as a member of your group for the purposes of our procedures within the Assembly".

A Conservative spokesman said: "Decisions about who sits with the Conservative group in the Welsh Assembly are a matter for the group in the Welsh Assembly."

His decision to join the Conservative group was warmly welcomed by Mr Davies.

"Mark's decision to join the group is testament to the strength and unity of the Welsh Conservative team in Cardiff Bay which provides the only real opposition to a tired and complacent Labour administration."